[Dnsmasq-discuss] PXE service across subnets

GARRISON, TRAVIS J. garrisot at otc.edu
Fri Dec 3 22:49:21 GMT 2010


>>>> We have tried searching but we could not find an answer to our 
>>>> problem. Our clients cannot pxe boot from our dnsmasq server across 
>>>> different subnets. We have the dnsmasq server configured to proxy 
>>>> the dhcp requests to our main dhcp server. We have created helper 
>>>> addresses for both the dhcp and pxe server on the different subnets. 
>>>> Pxe booting works fine when on the same network. What are we 
>>>> missing?
>>>>
>>>
>>> Is anything logged by dnsmasq? The DHCP helper function needs to 
>>> relay broadcasts to both servers. Are you sure that the switches can 
>>> do that?
>>
>> We did a packet capture on the dnsmasq server and tried to pxe boot 
>> one of our clients. We can see 3 DHCP Discover requests come in from 
>> the 172.25.16.0 subnet, which would be our client, but we see no 
>> response from the dnsmasq server. We have the option 
>> dhcp-range=172.25.16.0,proxy set. Our networks are in the
>> 255.255.252.0 subnet range, would that have any problems?
>>
>
>Ah, lightbulb. This extract from the man page is relevant:
>
>"For  directly connected  networks  (ie,  networks  on  which the machine running dnsmasq has an interface) the netmask is optional. It is, however, required for networks which receive DHCP service via a relay agent."
>
>So your dhcp-range line should be
>
>dhcp-range=172.25.16.0,proxy,255.255.252.0

Ah ha, that fixed it, thank you big time :)

Travis



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